Head pressurizing force adjusting device, image forming apparatus and method of adjusting head pressurizing force

Abstract

According to one embodiment, an image forming apparatus includes a first sensor, a second sensor, a first head, a first head pressurizing force adjusting device, a second head, a second head pressurizing force adjusting device, and a control unit. The first and second sensors detect a recording medium. The first head forms an image on a first surface of the recording medium and the second head forms an image on a second surface of the recording medium. The first head pressurizing force adjusting device adjusts a pressurizing force of the first head to the first platen and the second head pressurizing force adjusting device adjusts a pressurizing force of the second head to the second platen. The control unit controls the first head pressurizing force adjusting device and the second head pressurizing force adjusting device based on outputs of the first and second sensors.

What is claimed is: 
     
       1. A head pressurizing force adjusting device, comprising:
 a plurality of cams having different radiuses; 
 an arm configured to contact with the cams and be rotated with rotation of the cams; 
 a head which is opposed to a platen with a recording medium conveyance path interposed between the head and the platen; 
 a head support member configured to bring the head into contact with the platen when the arm is rotated by a radius having a first length of the cams, brings the head into contact with the platen with a contact pressure weaker than a contact pressure when the arm is rotated by the radius having the first length, with the head support member being separated from the arm as the arm is displaced in the opposite direction to the platen when the arm is rotated by a radius having a second length of the cams, and brings the head into contact with the platen with a contact pressure weaker than a contact pressure when the arm is rotated by the radius having the second length, with the arm being displaced in such a manner that the head is separated from the platen when the arm is rotated by a radius having a third length of the cams; 
 a first elastic member configured to bias the arm toward the head support member; and 
 a second elastic member configured to bias the head support member toward the platen. 
 
     
     
       2. The device of  claim 1 , further comprising:
 a sensor configured to detect a position of a recording medium; 
 a driving unit configured to rotate the cams; and 
 a control unit configured to drive the driving unit based on an output of the sensor. 
 
     
     
       3. The device of  claim 2 , wherein the control unit rotates the cams to separate the head from the platen when the recording medium is removed. 
     
     
       4. An image forming apparatus, comprising:
 a first sensor which is disposed in the downstream of a recording medium conveyance path and detects a recording medium; 
 a second sensor which is disposed in the upstream of the recording medium conveyance path and detects the recording medium; 
 a first head which is interposed between the first sensor and the second sensor in the opposite to a first platen with the recording medium conveyance path interposed between the first head and the first platen and forms an image on a first surface of the recording medium; 
 a first head pressurizing force adjusting device configured to adjust a pressurizing force of the first head to the first platen; 
 a second head which is interposed between the first head and the second sensor in the opposite to a second platen with the recording medium conveyance path interposed between the second head and the second platen and forms an image on a second surface of the recording medium; 
 a second head pressurizing force adjusting device configured to adjust a pressurizing force of the second head to the second platen; and 
 a control unit configured to control the first head pressurizing force adjusting device and the second head pressurizing force adjusting device based on outputs of the first and second sensors. 
 
     
     
       5. The apparatus of  claim 4 , wherein, if the first and second sensors detect the recording medium together when the recording medium is discharged, the control unit controls the first head to be separated from the first platen and the recording medium to be discharged with backward movement. 
     
     
       6. The apparatus of  claim 4 , wherein, if the first sensor detects the recording medium but the second sensor does not detect the recording medium when the recording medium is discharged, the control unit controls the second head to be separated from the second platen and the recording medium to be discharged with forward movement. 
     
     
       7. The apparatus of  claim 4 , wherein, if the first sensor does not detect the recording medium but the second sensor detects the recording medium when the recording medium is discharged, the control unit controls the first head to be separated from the first platen and the second head to be separated from the second platen. 
     
     
       8. The apparatus of  claim 4 , further comprising: a third sensor which is interposed between the first head and the second head and detects a black mark of the recording medium, wherein, when the recording medium is loaded, the control unit controls the recording medium to be moved forward with the first head pressed to the first platen, detects a page length of the recording medium based on an output of the third sensor, separates the first head from the first platen, and controls the recording medium to be moved backward to adjust a head page of the recording medium to a printable position. 
     
     
       9. The apparatus of  claim 4 , further comprising: a fourth sensor which is interposed between the first head and the second head and detects a label based on intensity of transmission light of the recording medium, wherein, when the recording medium is loaded, the control unit controls the recording medium to be moved forward with the first head pressed to the first platen, detects a leading end position of the label based on an output of the fourth sensor, separates the first head from the first platen, and controls the recording medium to be move backward to adjust a head label of the recording medium to a printable position. 
     
     
       10. The apparatus of  claim 4 , wherein the first head pressurizing force adjusting device includes:
 a plurality of first cams having different radiuses; 
 a first arm configured to contact with the first cams and is rotated with rotation of the first cams; 
 a first head which is opposed to a first platen with a recording medium conveyance path interposed between the first head and the first platen; 
 a first head support member configured to bring the first head into contact with the first platen when the first arm is rotated by a radius having a first length of the first cams, bring the first head into contact with the first platen with a contact pressure weaker than a contact pressure when the first arm is rotated by the radius having the first length, with the first head support member being separated from the first arm as the first arm is displaced in the opposite direction to the first platen when the first arm is rotated by a radius having a second length of the first cams, and bring the first head into contact with the first platen with a contact pressure weaker than a contact pressure when the first arm is rotated by the radius having the second length, with the first arm being displaced in such a manner that the first head is separated from the first platen when the first arm is rotated by a radius having a third length of the first cams; 
 a first one of first elastic members configured to bias the first arm toward the first head support member; and 
 a second one of the first elastic members configured to bias the first head support member toward the first platen, 
 wherein the second head pressurizing force adjusting device includes: 
 a plurality of second cams having different radiuses; 
 a second arm configured to contact with the second cams and is rotated with rotation of the second cams; 
 a second head which is opposed to a second platen with a recording medium conveyance path interposed between the second head and the second platen; 
 a second head support member configured to bring the first head into contact with the second platen when the second arm is rotated by a radius having a first length of the second cams, bring the second head into contact with the second platen with a contact pressure weaker than a contact pressure when the second arm is rotated by the radius having the first length, with the second head support member being separated from the second arm as the second arm is displaced in the opposite direction to the second platen when the second arm is rotated by a radius having a second length of the second cams, and bring the second head into contact with the second platen with a contact pressure weaker than a contact pressure when the second arm is rotated by the radius having the second length, with the second arm being displaced in such a manner that the second head is separated from the second platen when the second arm is rotated by a radius having a third length of the second cams; 
 a first one of second elastic members configured to bias the second arm toward the second head support member; and 
 a second one of the second elastic members configured to bias the second head support member toward the second platen. 
 
     
     
       11. A method of adjusting a head pressurizing force, the method, comprising:
 changing a pressurizing force of a plurality of heads, which is disposed along a recording medium conveyance path, to a plurality of platens by changing the number of elastic members biasing the heads toward the platens based on an output of a sensor detecting a position of a recording medium; 
 inputting outputs of a first sensor which is disposed in the downstream of a recording medium conveyance path and detects a recording medium and a second sensor which is disposed in the upstream of the recording medium conveyance path and detects the recording medium; 
 separating a first head from a first platen if the first and second sensors detect the recording medium together; and 
 discharging the recording medium with backward movement. 
 
     
     
       12. The method of  claim 11 , further comprising:
 separating a second head from a second platen if the first sensor detects the recording medium but the second sensor does not detect the recording medium when the recording medium is discharged; and 
 discharging the recording medium with forward movement. 
 
     
     
       13. The method of  claim 11 , further comprising:
 separating the first head from the first platen and a second head from a second platen if the first sensor does not detect the recording medium but the second sensor detects the recording medium when the recording medium is discharged. 
 
     
     
       14. The method of  claim 11 , further comprising:
 moving forward the recording medium with the first head pressed to the first platen; 
 detecting a page length of the recording medium based on an output of a third sensor which detects a black mark of the recording medium; 
 separating the first head from the first platen; and 
 moving backward the recording medium to adjust a head page of the recording medium to a printable position. 
 
     
     
       15. The method of  claim 11 , further comprising:
 moving forward the recording medium with the first head pressed to the first platen; 
 detecting a leading end position of a label of the recording medium based on an output of a fourth sensor which detects the label based on intensity of transmission light of the recording medium; 
 separating the first head from the first platen; and 
 moving backward the recording medium to adjust a head label of the recording medium to a printable position.